[en] Surface modified silica gels containing chemically bound molecules of the type = Si-O-Si(OH)sub(n) (C₆H₅)₃sub(-)sub(n) (n = 1,2) and = Si-O-Si(OH)₂ CH₂C₆H₅ have been investigated by ¹³C NMR. At low temperature (77 K) the signals from the phenyl carbons have a broad low-symmetric chemical shift dispersion, characteristic for a rigid molecule. At room temperature the dispersion is different and characteristic of an axial symmetric chemical shift anisotropy caused by molecular reorientations. The shape of the spectra has been calculated for different possible molecular reorientations and compared with the experimental spectra. From this analysis the reorientation which takes place in the molecules, as well as the orientation of the molecules relative to the surface, and the geometry of the surface-adsorbate bond were obtained. (orig.)